With this mod, you can give dragons the ability to breathe fire, each with its own unique characteristics

By default, it is compatible with all dragons from Dragon Mounts : Legacy and my addon Dragon Mounts Legacy : More Dragons.

If you have an addon for Dragon Mounts : Legacy, you can add your own dragon breaths using a data pack

you must create a file anyname.json in the path 

data/yourdatatapackname/dragon_breaths

{
  "dragon": "dragonmounts:forest",
  "color1": 1721356,
  "color2": 1456650,
  "setOnFire": false,
  "breathEffects": [
    {
      "mobEffect": "minecraft:poison",
      "duration": 100,
      "amplifier": 1
    }
  ]
}

dragon - must be the id of the dragon breed

color - the color of breath, mapinfo color you can get it here

setOnFire - if the breath burns